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<h1 >Storage Management</h1>
<p>
This page describes the backends for the storage management capabilities in
libvirt.
</p>
<ul>
<li>
<a href="#StorageBackendDir">Directory backend</a>
</li>
<li>
<a href="#StorageBackendFS">Local filesystem backend</a>
</li>
<li>
<a href="#StorageBackendNetFS">Network filesystem backend</a>
</li>
<li>
<a href="#StorageBackendLogical">Logical backend</a>
</li>
<li>
<a href="#StorageBackendDisk">Disk backend</a>
</li>
<li>
<a href="#StorageBackendISCSI">iSCSI backend</a>
</li>
<li>
<a href="#StorageBackendSCSI">SCSI backend</a>
</li>
<li>
<a href="#StorageBackendMultipath">Multipath backend</a>
</li>
</ul>
<h2><a name="StorageBackendDir">Directory pool</a></h2>
<p>
A pool with a type of <code>dir</code> provides the means to manage
files within a directory. The files can be fully allocated raw files,
sparsely allocated raw files, or one of the special disk formats
such as <code>qcow</code>,<code>qcow2</code>,<code>vmdk</code>,
<code>cow</code>, etc as supported by the <code>qemu-img</code>
program. If the directory does not exist at the time the pool is
defined, the <code>build</code> operation can be used to create it.
</p>
<h3>Example pool input definition</h3>
<pre>
<pool type="dir">
<name>virtimages</name>
<target>
<path>/var/lib/virt/images</path>
</target>
</pool></pre>
<h3>Valid pool format types</h3>
<p>
The directory pool does not use the pool format type element.
</p>
<h3>Valid volume format types</h3>
<p>
One of the following options:
</p>
<ul>
<li><code>raw</code>: a plain file</li>
<li><code>bochs</code>: Bochs disk image format</li>
<li><code>cloop</code>: compressed loopback disk image format</li>
<li><code>cow</code>: User Mode Linux disk image format</li>
<li><code>dmg</code>: Mac disk image format</li>
<li><code>iso</code>: CDROM disk image format</li>
<li><code>qcow</code>: QEMU v1 disk image format</li>
<li><code>qcow2</code>: QEMU v2 disk image format</li>
<li><code>vmdk</code>: VMWare disk image format</li>
<li><code>vpc</code>: VirtualPC disk image format</li>
</ul>
<p>
When listing existing volumes all these formats are supported
natively. When creating new volumes, only a subset may be
available. The <code>raw</code> type is guaranteed always
available. The <code>qcow2</code> type can be created if
either <code>qemu-img</code> or <code>qcow-create</code> tools
are present. The others are dependent on support of the
<code>qemu-img</code> tool.
</p>
<h2><a name="StorageBackendFS">Filesystem pool</a></h2>
<p>
This is a variant of the directory pool. Instead of creating a
directory on an existing mounted filesystem though, it expects
a source block device to be named. This block device will be
mounted and files managed in the directory of its mount point.
It will default to allowing the kernel to automatically discover
the filesystem type, though it can be specified manually if
required.
</p>
<h3>Example pool input</h3>
<pre>
<pool type="fs">
<name>virtimages</name>
<source>
<device path="/dev/VolGroup00/VirtImages"/>
</source>
<target>
<path>/var/lib/virt/images</path>
</target>
</pool></pre>
<h3>Valid pool format types</h3>
<p>
The filesystem pool supports the following formats:
</p>
<ul>
<li><code>auto</code> - automatically determine format</li>
<li>
<code>ext2</code>
</li>
<li>
<code>ext3</code>
</li>
<li>
<code>ext4</code>
</li>
<li>
<code>ufs</code>
</li>
<li>
<code>iso9660</code>
</li>
<li>
<code>udf</code>
</li>
<li>
<code>gfs</code>
</li>
<li>
<code>gfs2</code>
</li>
<li>
<code>vfat</code>
</li>
<li>
<code>hfs+</code>
</li>
<li>
<code>xfs</code>
</li>
</ul>
<h3>Valid volume format types</h3>
<p>
The valid volume types are the same as for the <code>directory</code>
pool type.
</p>
<h2><a name="StorageBackendNetFS">Network filesystem pool</a></h2>
<p>
This is a variant of the filesystem pool. Instead of requiring
a local block device as the source, it requires the name of a
host and path of an exported directory. It will mount this network
filesystem and manage files within the directory of its mount
point. It will default to using NFS as the protocol.
</p>
<h3>Example pool input</h3>
<pre>
<pool type="netfs">
<name>virtimages</name>
<source>
<host name="nfs.example.com"/>
<dir path="/var/lib/virt/images"/>
</source>
<target>
<path>/var/lib/virt/images</path>
</target>
</pool></pre>
<h3>Valid pool format types</h3>
<p>
The network filesystem pool supports the following formats:
</p>
<ul>
<li><code>auto</code> - automatically determine format</li>
<li>
<code>nfs</code>
</li>
</ul>
<h3>Valid volume format types</h3>
<p>
The valid volume types are the same as for the <code>directory</code>
pool type.
</p>
<h2><a name="StorageBackendLogical">Logical volume pools</a></h2>
<p>
This provides a pool based on an LVM volume group. For a
pre-defined LVM volume group, simply providing the group
name is sufficient, while to build a new group requires
providing a list of source devices to serve as physical
volumes. Volumes will be allocated by carving out chunks
of storage from the volume group.
</p>
<h3>Example pool input</h3>
<pre>
<pool type="logical">
<name>HostVG</name>
<source>
<device path="/dev/sda1"/>
<device path="/dev/sdb1"/>
<device path="/dev/sdc1"/>
</source>
<target>
<path>/dev/HostVG</path>
</target>
</pool></pre>
<h3>Valid pool format types</h3>
<p>
The logical volume pool does not use the pool format type element.
</p>
<h3>Valid volume format types</h3>
<p>
The logical volume pool does not use the volume format type element.
</p>
<h2><a name="StorageBackendDisk">Disk volume pools</a></h2>
<p>
This provides a pool based on a physical disk. Volumes are created
by adding partitions to the disk. Disk pools are have constraints
on the size and placement of volumes. The 'free extents'
information will detail the regions which are available for creating
new volumes. A volume cannot span across 2 different free extents.
</p>
<h3>Example pool input</h3>
<pre>
<pool type="disk">
<name>sda</name>
<source>
<device path='/dev/sda'/>
</source>
<target>
<path>/dev</path>
</target>
</pool></pre>
<h3>Valid pool format types</h3>
<p>
The disk volume pool accepts the following pool format types, representing
the common partition table types:
</p>
<ul>
<li>
<code>dos</code>
</li>
<li>
<code>dvh</code>
</li>
<li>
<code>gpt</code>
</li>
<li>
<code>mac</code>
</li>
<li>
<code>bsd</code>
</li>
<li>
<code>pc98</code>
</li>
<li>
<code>sun</code>
</li>
</ul>
<p>
The <code>dos</code> or <code>gpt</code> formats are recommended for
best portability - the latter is needed for disks larger than 2TB.
</p>
<h3>Valid volume format types</h3>
<p>
The disk volume pool accepts the following volume format types, representing
the common partition entry types:
</p>
<ul>
<li>
<code>none</code>
</li>
<li>
<code>linux</code>
</li>
<li>
<code>fat16</code>
</li>
<li>
<code>fat32</code>
</li>
<li>
<code>linux-swap</code>
</li>
<li>
<code>linux-lvm</code>
</li>
<li>
<code>linux-raid</code>
</li>
<li>
<code>extended</code>
</li>
</ul>
<h2><a name="StorageBackendISCSI">iSCSI volume pools</a></h2>
<p>
This provides a pool based on an iSCSI target. Volumes must be
pre-allocated on the iSCSI server, and cannot be created via
the libvirt APIs. Since /dev/XXX names may change each time libvirt
logs into the iSCSI target, it is recommended to configure the pool
to use <code>/dev/disk/by-path</code> or <code>/dev/disk/by-id</code>
for the target path. These provide persistent stable naming for LUNs
</p>
<h3>Example pool input</h3>
<pre>
<pool type="iscsi">
<name>virtimages</name>
<source>
<host name="iscsi.example.com"/>
<device path="demo-target"/>
</source>
<target>
<path>/dev/disk/by-path</path>
</target>
</pool></pre>
<h3>Valid pool format types</h3>
<p>
The iSCSI volume pool does not use the pool format type element.
</p>
<h3>Valid volume format types</h3>
<p>
The iSCSI volume pool does not use the volume format type element.
</p>
<h2><a name="StorageBackendSCSI">SCSI volume pools</a></h2>
<p>
This provides a pool based on a SCSI HBA. Volumes are preexisting SCSI
LUNs, and cannot be created via the libvirt APIs. Since /dev/XXX names
aren't generally stable, it is recommended to configure the pool
to use <code>/dev/disk/by-path</code> or <code>/dev/disk/by-id</code>
for the target path. These provide persistent stable naming for LUNs
<span class="since">Since 0.6.2</span>
</p>
<h3>Example pool input</h3>
<pre>
<pool type="scsi">
<name>virtimages</name>
<source>
<adapter name="host0"/>
</source>
<target>
<path>/dev/disk/by-path</path>
</target>
</pool></pre>
<h3>Valid pool format types</h3>
<p>
The SCSI volume pool does not use the pool format type element.
</p>
<h3>Valid volume format types</h3>
<p>
The SCSI volume pool does not use the volume format type element.
</p>
<h2><a name="StorageBackendMultipath">Multipath pools</a></h2>
<p>
This provides a pool that contains all the multipath devices on the
host. Volume creating is not supported via the libvirt APIs.
The target element is actually ignored, but one is required to appease
the libvirt XML parser.<br/>
<br/>
Configuring multipathing is not currently supported, this just covers
the case where users want to discover all the available multipath
devices, and assign them to guests.
<span class="since">Since 0.7.1</span>
</p>
<h3>Example pool input</h3>
<pre>
<pool type="mpath">
<name>virtimages</name>
<target>
<path>/dev/mapper</path>
</target>
</pool></pre>
<h3>Valid pool format types</h3>
<p>
The Multipath volume pool does not use the pool format type element.
</p>
<h3>Valid volume format types</h3>
<p>
The Multipath volume pool does not use the volume format type element.
</p>
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